Related to Mondays post on core competences, it's worth mentioning that there are instances where deviating from your core competency can be a good idea. In fact, some businesses are able to leverage their initial core competency to enter entirely new businesses. And in some cases those businesses have become the major driver of profits.
One example of this was General Motors. Everybody knows that General Motors' core competency was making and marketing automobiles. What many people don't know is that back in the early 2000s, most of their profit was generated by their financing arm, GMAC. So in reality, their core competency wasn't making cars, it was lending people money to buy cars. GMAC was eventually spun off; likely to allow GM to put their focus back on making and marketing cars, and because the car business was dragging down the value of the financing business.

Lots of other businesses find that financing can be more profitable than their core business. Every time I go to a clothing store like Banana Republic they practically beg me to sign up for their store credit card. They're willing to give consumers huge discounts on their clothes (their core product) just to get them to sign up for their credit card. Sure, they probably have found that their credit card carrying customers are more loyal and buy more clothing when they shop, but I guarantee a large portion (in some cases, a majority) of these stores' profits comes from their credit card businesses.

Another example of an industry that has deviated from its core competency is higher education. Large schools like Harvard have found that they make a lot more money managing their endowments than they do selling tuition. Depending on the year, Harvard’s endowment has made 5, 10 or even 20 times more than they've made in total annual tuition. Further, in 2004, Harvard’s top five endowment managers made $78 million in annual compensation – that's 100 times more than the school's president made in the same year.

Of course there's nothing wrong with using your core competency to create a second, more profitable business. It reduces business risk and contributes to growth. Shareholders love it. But it can reduce focus.

As I wrote on Monday, trying to be good at too many things is dangerous. And when you get too big, putting your focus in too many places puts the thing that you do really well at risk. And losing focus on that thing is even scarier when that thing is propping up an even more profitable business.